1. Field of the Invention
The present invention relates to a silane-terminated polyurethane, a process for its preparation and its use.
2. Discussion of the Background
In the building industry, joints serve for compensating movements between individual structural elements. Such movements are caused, for example, by thermal expansion or settling processes. As a rule, joints are sealed using sealing compounds, for example according to DIN EN ISO 1 1600. In addition to the sealing function, sealing compounds must also compensate movements due to elastic deformation. Base polymers used for the preparation of the sealing compounds are silicones, acrylates, butyl rubbers, polysulfides, polyurethanes and MS polymers. Silane-crosslinking polyurethanes are new for this application.
The reaction of secondary aminosilanes with isocyanate-containing polyurethane prepolymers leads to silane-terminated polyurethanes which can be crosslinked by means of moisture. The crosslinking of corresponding sealing compounds and adhesive materials can be accelerated by adding a catalyst.
Conventional isocyanate-containing polyurethane prepolymers are generally obtained from polyols, which are mostly synthesized from ethylene oxide and/or propylene oxide, and aliphatic or aromatic isocyanates.
The reaction of isocyanate-containing polyurethane prepolymers with aliphatic or aromatic secondary aminosilanes is catalyzed by tin compounds. The reaction gives silane-terminated polyurethanes for adhesive and sealant applications, as described, for example, in EP 0 676 403 A1.
Alternatively, isocyanatosilanes, such as, for example, OCNxe2x80x94(CH2)3Si(X)3, where X is an alkoxy group, such as methoxy or ethoxy, can also be reacted with hydroxyl-containing polyurethane prepolymers to give silane-terminated polyurethanes (U.S. Pat. No. 4,345,053). No gaseous byproduct is liberated during the silane crosslinking, compared to the case of the classical urethane crosslinking. Thus, isocyanate-free systems, such as coating compositions, finishes, adhesives and sealing compounds can be substantially safely formulated since volatile isocyanate monomers, e.g. tolylene diisocyanate (TDI), are suspected of being very harmful to health.
It is the object of the present invention to provide an improved silane-terminated polyurethane, in particular for adhesive and sealant applications.
This and other objects are achieved according to the present invention, the first embodiment of which includes an adhesive material or sealing compound, comprising: a metal-free silane-terminated polyurethane.
A further embodiment includes a method of making an adhesive material or sealing compound, comprising:
mixing a metal-free silane-terminated polyurethane polyurethane with a plasticizer and optionally a filler.
Another embodiment of the present invention includes a metal-free silane-terminated polyurethane, obtained by reacting at least one aliphatic secondary aminoalkylalkoxysilane of formula (Ia)
Rxe2x80x94NHxe2x80x94(CH2)3Si(R1)x(OR2)(3-x)xe2x80x83xe2x80x83(Ia) 
or at least one aliphatic secondary aminoalkylalkoxysilane of formula (Ib)
Rxe2x80x94NHxe2x80x94CH2xe2x80x94CH(R1)xe2x80x94CH2xe2x80x94Si(R1)x(OR2)(3-x)xe2x80x83xe2x80x83(Ib) 
wherein in formulae (Ia) and (Ib), R is a linear or branched alkyl group having 1 to 18 C atoms, R1 is a methyl group, R2 is a methyl or ethyl group and x is 0 or 1,
with a polyurethane prepolymer in the absence of a metal catalyst;
wherein the polyurethane prepolymer has at least one terminal isocyanate group.
In yet another embodiment the present invention relates to a process for the preparation of a metal-free silane-terminated polyurethane, comprising:
reacting at least one aliphatic secondary aminoalkylalkoxysilane of formula (Ia)
Rxe2x80x94NHxe2x80x94(CH2)3Si(R1)x(OR2)(3-x)xe2x80x83xe2x80x83(Ia) 
or at least one aliphatic secondary aminoalkylalkoxysilane of formula (Ib)
Rxe2x80x94NHxe2x80x94CH2xe2x80x94CH(R1)xe2x80x94CH2xe2x80x94Si(R1)x(OR2)(3-x)xe2x80x83xe2x80x83(Ib) 
wherein in the formulae (Ia) and (Ib), R is a linear or branched alkyl group having 1 to 18 C atoms, R1 is a methyl group, R2 is a methyl or ethyl group and x is 0 or 1:
with a polyurethane prepolymer in the absence of a metal catalyst;
wherein the polyurethane prepolymer carries at least one terminal isocyanate group.
Surprisingly, it was found that the reaction of an aliphatic secondary aminosilane of formulae (Ia) or (Ib) with an isocyanate-containing polyurethane prepolymers in the absence of a metal catalyst, in particular of a tin catalyst, leads to a colorless and low-viscosity silane-terminated polyurethane:
Rxe2x80x94NHxe2x80x94(CH2)3Si(R1)x(OR2)(3-x)xe2x80x83xe2x80x83(Ia) 
or at least one aliphatic secondary aminoalkylalkoxysilane of formula (Ib)
Rxe2x80x94NHxe2x80x94CH2xe2x80x94CH(R1)xe2x80x94CH2xe2x80x94Si(R1)x(OR2)(3-x)xe2x80x83xe2x80x83(Ib) 
wherein in formulae (Ia) and (Ib), R is a linear or branched alkyl group having 1 to 18 C atoms, R1 is a methyl group, R2 is a methyl or ethyl group and x is 0 or 1.
A metal catalyst, such as, for example, dibutyltin dilaurate (DBTL), is not necessary for the present silane termination reaction. This is advantageous because the thermal cleavage of xe2x80x94NRxe2x80x94COxe2x80x94NRxe2x80x94 groups is promoted in particular by a high content of tin compounds.
According to the present invention, a low-viscosity, metal-free silane-terminated polyurethane can be formulated in a simple and economical manner with a further additive, such as a filler, a plasticizer, a thixotropic agent, a stabilizer, a pigment, etc., to give an adhesive or a sealing compounds.
In addition, the productivity of the prepolymer preparation increases due to the shorter pot lives in the silane termination reaction.
Moreover, a silane-terminated polyurethane prepared according to the present invention is particularly environmentally compatible because it is substantially free of residues of metal catalysts, i.e. metal-free.
The rapid reaction of an isocyanate group of the polyurethane prepolymer with a secondary aliphatic aminosilane of formulae (Ia) or (Ib) is preferred in the preparation of the silane-terminated polyurethane. Preferably DYNASYLAN(copyright) 1189 is used as secondary aliphatic aminosilane. The reaction proceeds according to the equation:
prepolymer-NCO+nBuxe2x80x94NHxe2x80x94(CH2)3xe2x80x94Si(OMe)3xe2x86x92prepolymer-NHxe2x80x94CO-nBuNxe2x80x94(CH2)3xe2x80x94Si(OMe)3. 
The possible, but undesired, chain-lengthening secondary reactionxe2x80x94undesired because it increases the viscosityxe2x80x94is not observed in the process according to the invention. Thus, the chain-lengthening secondary reaction is effectively suppressed:
prepolymer-NHxe2x80x94CO-nBuNxe2x80x94(CH2)3Si(OMe)3+prepolymer-NCOxe2x86x92prepolymer-N(COxe2x80x94NH-prepolymer)-CO-nBuNxe2x80x94(CH2)3xe2x80x94Si(OMe)3. 
The present invention thus relates to a metal-free, in particular tin-free, silane-terminated polyurethane for an adhesive material or a sealing compound.
The present invention furthermore relates to a metal-free silane-terminated polyurethane which is obtained by reacting at least one aliphatic secondary aminoalkylalkoxysilane of formula (Ia)
Rxe2x80x94NHxe2x80x94(CH2)3Si(R1)x(OR2)(3-x)xe2x80x83xe2x80x83(Ia) 
or at least one aliphatic secondary aminoalkylalkoxysilane of formula (Ib)
Rxe2x80x94NHxe2x80x94CH2xe2x80x94CH(R1)xe2x80x94CH2xe2x80x94Si(R1)x(OR2)(3-x)xe2x80x83xe2x80x83(Ib) 
wherein in the formulae (Ia) and (Ib), R is a linear, branched or cyclic alkyl group preferably cyclohexyl, having 1 to 18 C atoms, preferably having 1 to 6 C atoms, R1 is a methyl group, R2 is a methyl or ethyl group and x is 0 or 1,
with a polyurethane prepolymer having at least one terminal isocyanate group in the absence of a metal catalyst.
Preferably, the reaction of the aliphatic secondary aminoalkylalkoxysilane with the polyurethane prepolymer is carried out in the absence of a tin catalyst. Conventionally, dibutyltin dilaurate (DBTL) or another dialkyltin dicarboxylate compound is used as a tin catalyst.
Preferred secondary aminoalkylalkoxysilanes are N-(n-butyl)-3-aminopropyltrimethoxysilane, N-(n-butyl)-3-aminopropyltriethoxysilane, N-(n-butyl)-3-aminopropylmethyldimethoxysilane, N-(n-butyl)-3-aminopropylmethyldiethoxysilane, N-(n-butyl)-3-amino-2-methylpropyltrimethoxysilane, N-(n-butyl)-3-amino-2-methylpropyltriethoxysilane or N-ethyl-3-amino-2-methylpropyltrimethoxysilane.
Within the meaning of the present invention a polyurethane prepolymer is defined as a reaction product of a diol, for example a so-called polyetherpolyol, such as a polyethylene oxide or a polypropylene oxide, having a terminal hydroxyl group and a molecular weight of from 200 to 2000 g/mol, or a polyol, i.e. a polyetherpolyol or a polyesterpolyol, or a mixture thereof and at least one diisocyanate. Preferably, an excess of diisocyanate is used so that the polyurethane prepolymer contains a terminal isocyanate (NCO) group. The diol/polyol component of the polyurethane prepolymer may have both a polyether and a polyester structure of variable molecular weight.
Both aliphatic compounds, e.g. isophorone diisocyanate (IPDI) or hexamethylene diisocyanate (HDI), and aromatic compounds, e.g. tolylene diisocyanate (TDI) or diphenylmethane diisocyanate (MDI) are preferred for use as diisocyanates.
According to the invention, a polyurethane prepolymer based on an aliphatic diisocyanate, preferably isophorone diisocyanate (IPDI) or hexamethylene diisocyanate (HDI), is furthermore preferred. Diphenylmethane diisocyanate (MDI) is preferred as polyurethane prepolymer based on an aromatic diisocyanate.
In addition, the present invention relates to the process for the preparation of a metal-free silane-terminated polyurethane, in which at least one aliphatic secondary aminoalkylalkoxysilane of formula (Ia)
xe2x80x83Rxe2x80x94NHxe2x80x94(CH2)3Si(R1)x(OR2)(3-x)xe2x80x83xe2x80x83(Ia)
or at least one aliphatic secondary aminoalkylalkoxysilane of formula (Ib)
Rxe2x80x94NHxe2x80x94CH2xe2x80x94CH(R1)xe2x80x94CH2xe2x80x94Si(R1)x(OR2)(3-x)xe2x80x83xe2x80x83(Ib) 
wherein in the formulae (Ia) and (Ib), R is a linear or branched alkyl group having 1 to 18 C atoms, R1 is a methyl group, R2 is a methyl or ethyl group and x is 0 or 1,
is reacted with a polyurethane prepolymer having a terminal isocyanate group in the absence of a metal catalyst. The metal-free, preferably tin-free, silane-terminated polyurethane according to the invention is preferably used for adhesive and sealant applications.
Preferably, the process according to the invention is carried out as follows:
An anhydrous mixture of polyetherdiol and polyethertriol can be mixed with a diisocyanate at from about 30 to 40xc2x0 C. to prepare the prepolymer. The reaction is preferably carried out under inert gas and under exclusion of water. Preferably, the mixture is allowed to react at about 70xc2x0 C. until a constant isocyanate (NCO) content is reached. Preferably, the NCO content is analyzed during the reaction. The reaction mixture may furthermore contain a diluent or solvent, which is preferably inert, for example toluene. Depending on the NCO content, a secondary aminosilane can now be added.
The reaction of the polyurethane prepolymer with the secondary aminosilane is preferably carried out at from 25 to 80xc2x0 C. The secondary aminosilane is preferably added in an excess of from 5 to 25 mol %.
The batch is preferably stirred at a temperature in the range of from 60 to 75xc2x0 C., in particular at about 70xc2x0 C., until NCO is no longer detectable.
Furthermore, a xe2x80x9cwater scavengerxe2x80x9d, for example an organofunctional alkoxysilane, preferably vinyltrimethoxysilane or vinyltriethoxysilane, may be added to the reaction mixture.
A metal catalyst-free, silane-terminated polyurethane according to the invention, which can advantageously be used as a starting material in formulations for adhesive and sealant applications, is thus obtained.
Products according to the invention are usually colorless and have a low viscosity.
Commercial comparative products, i.e. polyurethanes according to the prior art (see Comparative Example), generally have a viscosity in the range from 30 000 to 60 000 mpaxc2x7s.
In comparison, polyurethanes according to the invention preferably have a viscosity of from 12 000 to 25 000 mpaxc2x7s, particularly preferably from 15 000 to 20 000 mpaxc2x7s (viscosity values at 25xc2x0 C. according to DIN 53 015).
Silane-terminated polyurethanes according to the invention can be used for the preparation of formulations for adhesive and sealant applications. The silane-terminated polyurethane according to the invention can be used as base material. For this purpose, the polyurethane is initially introduced and is first mixed with plasticizer. This is preferably followed by incorporation of the filler with subsequent degassing of the material. Drying it agent, adhesion promoter and other additives can then be added. The material is usually thoroughly mixed and filled into cartridges or other suitable carriers.
Adhesives and sealing compounds based on silane-terminated polyurethanes preferably also contain the following components in addition to the silane-terminated polyurethanes:
a filler and/or pigment, a plasticizer, a drying agent, an adhesion promoter, a Theological additive, for example for producing thixotropic properties, a stabilizer and a preservative.
Having generally described this invention, a further understanding can be obtained by reference to certain specific examples which are provided herein for purposes of illustration only, and are not intended to be limiting unless otherwise specified.